[stevebrot]

...What made you go for the Katz rather than trying the *iST screen - did you specifically want a split image as opposed to just wanting a better screen ?

I went with the Katz Eye because I wanted the focus aids and was willing to spend the extra money in the interest of better customer service. I have not compared the eBay or focusingscreen.com products, but the general consensus is that the quality from both those sources is good. There are also several forum members who have successfully cannibalized an older 35mm camera and cut the screen down themselves. At this point, after having owned both Optibrite and non-Optibrite Katz Eye screens, I would suggest that the buyer look at the cheaper options unless they really think they need the Optibrite treatment.

Steve

[dave9t5]

Hi Dave - I was using MF only , not using AF to confirm focus.

I focused just once for the first shot,. I then didnt touch it again

Squier,

I happened to spend the better part of today calibrating a split-image focus-screen using a ruler. I took about 100 test shots. (Note: Body was K-m. Used a tripod and 2s timer.)

Here are some things I learned:

- Repetition. I ended up repeating my focus test at least 3 or 4 times per condition. Even with a split-image screen and a f/1.4 lens and a 1.2x eyepiece magnifier I occasionally had 3 different results from 3 different focusing attempts (sometimes I would have FF, BF, FF). That tells me that even with those precise focusing aids and narrow viewfinder DOF, my eye was not good enough to focus 100%. (Also see below about focusing direction.) Therefore, with the stock-screen and/or less bright lenses the accuracy will be less.

- The test should be done at the minimum focus distance of the lens. The reasons are (i) the farther something is away then the greater DOF at a given distance and (ii) it's hard to see the ruler when it is far away. Even at 1:7 magnification (typical minimum focus distance of 50/1.4mm lens), the 1cm increments on a ruler are pretty small in the viewfinder and I had trouble getting repeatable results. With DA35/2.8 macro lens, when I tried to test it at a similar magnification as the 50/1.4 I again had variable results. But at 1:1 it was much easier because the DOF was narrower and the ruler-lines appeared larger.

- Absolute BF/FF measurements with a ruler have meaning only at a given magnification. For example, at 1:7 I might see a FF/BF variation of up to 10mm which seems a lot. But at 1:1, I would see a variation of <1mm.

- FF/BF can vary by lens (and by zoom position). I used 5 different prime lenses (DA35/2.8, A50/1.4, VL58/1.4, K135/2.5, K24/2.8) and one zoom at 2 lengths (DAL18-55@35 and @55). For example, the DA35 consistently BF'd versus the A50/1.4. Another example, the DAL @55 consistently BF'd versus @35. (I don't know what to make of this. I knew that AF lenses could have variations in FF/BF, but I thought with MF that WYSIWYG. Maybe because the greater DOF's (f/2.8 vs. f/1.4 and f/5.6 vs. f/4.5), I couldn't tell? )

- Focusing direction makes a difference! I found that if I started focusing starting from from minimum distance direction, then I would be more likely to front-focus. If I focused starting from infinity direction, then I would be more likely to back-focus. The greater the DOF in the viewfinder, the worse this should be. Try focusing test 3x from both direction, see what happens. I didn't notice this until close to the end of my test sequence, so it's annoying I can't eliminate that variable because each focus test was uncontrolled in direction. However, I would usually go back and forth (like an AF lens, whirr, whirr, whirr)...but it's possible I didn't always which would account for the outliers in my data.


In conclusion:

1) There are a lot of ways to skew a focusing-test.

2) Even on a calibrated system, a very small amount of BF/FF is difficult to avoid. With 50/1.4 lens at f/1.4 and 1:7x, about 5~7mm is something I could live with because under the most controlled conditions I can't do better than that.

[Marc Sabatella]

Thanks for the reply Marc, but i take it you didnt read my first post too well, ( happens on forums a lot ) other wise you would have seen that i used a tripod and a remote cable

You're right; I missed that - sorry. But my point about DOF and hoe the viewfinder lies about it still stands. It's a very real and very significant effect, but it is possible to learn to work with it once you see the effect in action for yourself and understand what is going on.

[Squier]

Thanks Stevebrot - i'm veering more towards an *ist screen first, and if not satisfied, will probably plump for a Chinese split image, though out of all those sellers, Jinfinance , Cowey, VirtualVillage, Focusing.com , i havent decided who's best ...thought Focusing.com has a much greater choice and look more professional


Dave - thanks for that info - it seems more of a problem close up, so maybe i'll just have to live with it. My main joy is birds and animals, and therefore will be largely shooting at much smaller aps


Marc - i agree with you bud, and i'm sure i;ve done nothing conclusive, it just a bit of a shock

I tried to even out the variables a bit, by focusing once, and using a tripod and remote, but the conclusions are still patchy

[Parallax]

.................................f you look at the that first shot, the crispest point is the number 9, with more in focus behind the 9 than there is in front of the 9. This i would expect, but i was focusing on the number 7. There is no in-focus point ahead of the 7.

So isnt the camera back focusing on the 9 instead ?
.............................................

That would depend on whether you are talking about the 7cm mark or the 7 inch mark. Your initial post didn't say:

Focus point was on number 7 of the ruler, well as acurately as i could get the 7 inside the centre of the big circle.

[Squier]

Messed up

Its the 7 along the inch marks on the left

[Parallax]

Messed up

Its the 7 along the inch marks on the left

No, you didn't mess up. UK vs U.S. is all. You assumed CM, I assumed inch. Life would be much simpler if the U.S. had adopted the metric system like most of the rest of the world.

[Squier]

No probs - we still drive on the left

[Squier]

I did another quickie - but this time, i took my bifocul glasses off ( i'm blind at distance as well as close up )

So i re-adjusted the diopter for someone without glasses, but of course i have to wear them when i'm not looking through the viewfinder, then take them off to focus

I used the same parameters. EG tripod, remote cable SMC-A 500mm @ f1.7

Focused on the number 7 on the left hand side, which is the inches side. The result is quite astonishing. Does this mean my diopter was lying to me before ?


I also tried some other lenses of varying spec - Panagor 90mm macro , Tamron 70-210mm, and got much better results than the first test.

The SMC -A was spot on the 7, the Panagor 90mm ( fabulously sharp lens ) was also crisp on the 7, the Tamron was a tiny bit in front.

So, is it still worth upgrading the screen, given this new info ?

Its a bit of a pain to keep removing my glasses, and then putting them back etc , but if this means focused photos, i'll happily do this.

[Parallax]

I think this shows that there is no problem with the camera. (I didn't mean that the way it sounded!). I find that with my progressive lens glasses I have to do one of two things to MF accurately. I have to be VERY careful to look through the exact part of the eyeglass lens that the diopter adjustment is set for, or take my glasses off and adjust the diopter for my naked eye. The latter method works best, but as I do have some degree of astigmatism, MF is still somewhat of a crap shoot. I tried a Katz Eye and though it worked exactly as it should I found the split part difficult to use. The the microprism ring was much more useful. I e-mailed them to see if they could do one without the split, just a complete microprism center ring. Unfortunately, they said they couldn't at this time. I ended up putting the stock screen back in. If you are getting reproducible results with multiple lenses then I would heed the old adage: "If it aint broke, don't Fu(ss) with it."

EDIT: I see you used the proper side of the ruler this time.

[Squier]

The proper side of the ruler ( inches ) was always used ... the first tests were on the inches side, as was this one

Well i still wouldnt mind a brighter screen, EG maybe an *ist screen, but i dont think i'll bother with all that " debug " stuff and re-setting the focus in firmware

[Quension]

i dont think i'll bother with all that " debug " stuff and re-setting the focus in firmware

I think there was some confusion about this anyway, so to (hopefully) help clear it up:

That menu, and the BF/FF problems people talk about, relate to the autofocus system only. Firmware tweaks can't change the physical focus point, nor what you see through the adjustable viewfinder, which is what you rely on when manually focusing.

For manual focus issues, you would normally start by focusing according to the captured images (with AF and an appropriate test chart if possible, MF trial & error along with the AF hint indicator if not), ignoring what the viewfinder shows you. Once you determine the focus point the camera is capturing, work on diopter and focus screen issues to make what you see in the viewfinder match what the camera captures.

IOW, the viewfinder needs to be tuned to the camera's sensor, not the other way around. The viewfinder can't be considered a stable reference point on its own, simply because it's adjustable.

There could still be some defect in that part of the camera, of course, it's just not the BF/FF issue the whole debug thing is about, and can only be fixed via physical means

[Marc Sabatella]

Does this mean my diopter was lying to me before ?

Not the diopter - the focus screen, as I have explained several times now. I wasn't making it up then, an I'm not making it up. What I have completely explains everything you are seeing here. The viewfinder you more in focus than actually will be when using apertures of f/2.8 or greater. That's the way it is and always will be, and the trick to focus is accepting that and learning to work with it.

Its a bit of a pain to keep removing my glasses, and then putting them back etc , but if this means focused photos, i'll happily do this.

Random coincidence. The fact that the focus screen shows you too much in focus is true whether you use glasses or not. So until you accept and learn to work with this, you'll always have some shot you thought were in focus turn out not to be.

Actually, even after you accept and learn to work with it, you'll have have OOF shots sometimes - but you'll be able to get them in focus more often.

[OregonJim]

Not the diopter - the focus screen, as I have explained several times now.

I wonder if the effective f/2.8 maximum aperture of the focus screen is due to the light loss through the partially silvered mirror?

If one were to tape the backside of the mirror (thereby giving up autofocus), I wonder if the viewfinder image would be brighter?

[res3567]

At this point, after having owned both Optibrite and non-Optibrite Katz Eye screens, I would suggest that the buyer look at the cheaper options unless they really think they need the Optibrite treatment.

Steve

Is it worth the extra money for the Optibrite?Can you SEE the difference? Does it help the camera focus in low light?